Until very recently, scientists presumed (and it’s not clear that there were many experiments to support this) that our brain had a stopwatch of sorts built into its machinery. By stopwatch, scientists meant some biological system that created some signal at regular intervals. If this were true, we would be equally good at estimating short and long periods of time, but that’s totally not the case. Humans are pretty awful at guessing how long extended periods of time are.

Instead, Dean Buonomano at UCLA proposed in 2007 that our brains tell time in a different way. To steal his analogy, imagine a rock being tossed into a lake, which creates a series of ripples in the surface of the water. If you were to throw a second rock in, the ripples from the two rocks would interact with each other. The pattern of this interaction depends on the time between the two rocks hitting the lake. The firing of neurons (the rocks hitting the lake) create these unique patterns in their signals—and neurons can use the different patterns of signals interacting to tell time between events. The wonderful piece of this theory is that it explains why we’re good at telling time over short durations, but not long ones—over a long time, the ripples in the water just fade away.